Nondestructive method for measuring states of surface and apparatus for carrying out said method

ABSTRACT

A beam of parallel rays which emerges from a perpendicular object-grid is reflected from a mirror surface and transmitted through a centered optical system to a Lummer dividing cube located at the image focal point of said system so as to produce a direct beam which is focused onto a photoelectric cell after passing through an image-grid and a beam which is deflected at right-angles and focused onto a second photoelectric cell. The image-grid is displaced transversely so as to stop light from the object-grid and the mirror surface is replaced by the surface to be studied. The quotient of the indications given by the two balanced photoelectric cells is characteristic of a given state of surface. The indication given by the deflected-beam cell provides the albedo of a given surface state and color.

United States Patent Denis et al.

[ 1 May 16,1972

Grenoble; Roger H. Guicherd, Rue du Mail, 38 Saint-Egreve, both ofFrance [22] Filed: Jan.5, 1971 [21] Appl.No.: 103,994

[30] Foreign Application Priority Data Jan. 6, I970 France ..7000205[52] US. Cl. ..356/l20, 250/237 G, 356/209 [51 Int. Cl. ..G0lb 11/30[58] Field ofSearch ..356/109, l20, 167, 169;

[56] References Cited UNlTED STATES PATENTS 3,544,220 12/1970 Kaye..356/l09 Primary Examiner-William L. Sikes Assistant E.taminer-OrvilleB. Chew, ll AnorneyCameron, Kerkam & Sutton [57] ABSTRACT A beam ofparallel rays which emerges from a perpendicular object-grid isreflected from a mirror surface and transmitted through a centeredoptical system to a Lummer dividing cube located at the image focalpoint of said system so as to produce a direct beam which is focusedonto a photoelectric cell after passing through an image-grid and a beamwhich is deflected at right-angles and focused onto a secondphotoelectric cell. The image-grid is displaced transversely so as tostop light from the object-grid and the mirror surface is replaced bythe surface to be studied. The quotient of the indications given by thetwo balanced photoelectric cells is characteristic of a given state ofsurface. The indication given by the deflectedbeam cell provides thealbedo of a given surface state and color.

2 Claims, 1 Drawing Figure NONDESTRUCTIVE METHOD FOR MEASURING STATES OFSURFACE AND APPARATUS FOR CARRYING OUT SAID METHOD This inventionrelates to a method of nondestructive measurement of states of surfacesas well as to an apparatus for carrying out said method.

It is already a known practice to make use of a probe having acalibrated tip which is displaced over the surface under study along agenerator-line in the case of cylinders and at right angles to thedirection of machining in the case of flat plates.

Probes of this type are fairly accurate but nevertheless have adisadvantage in that they permit determination of the state of surfaceonly along a line. While this is an acceptable test in the case of amachined part having a constant or repetitive flaw, it is a method whichcannot be applied to rolled or drawn plates having randomly distributeddefects or flaws which entail the need for scanning of a small area andnot solely along a line.

This invention is directed to a nondestructive method for measuring thestate of surfaces which consists in projecting at an oblique angle ontoa substantially flat portion of surface constituting an approximatelyperfect mirror a beam of parallel rays of stabilized intensity acrosswhich is placed a socalled object-grid at right angles to the axis ofsaid beam, in placing a centered optical system across the reflectedbeam of parallel rays and at right angles to the axis thereof, inplacing a Lummer dividing cube at the downstream focal point or imagefocal point of said centered system, the effect of said Lummer cubebeing to emit two beams having the same light intensity, one beam beingdirect in the line of extension of the incident beam and the other beambeing deflected through 90 with respect to the first, in placing acrosssaid direct beam and at right angles to the principal axis thereof, aso-called imagegrid which is identical with the object-grid and capableof small displacements in its plane, the two grids being located in theanti-principal planes of said centered optical system, said image-gridbeing locked in position so as to permit the light beams emitted by theobject-grid to pass exactly through said image-grid, in focusing saiddirect beam and said deflected beam each onto a photoelectric cell, saidtwo cells being so adjusted as to supply equal currents under the actionof the light beam which falls on the Lummer cube, in displacing theimage-grid in its plane so as to stop all the light beams emitted by theobject-grid, and in replacing the portion of surface which performs thefunction of a perfect mirror by the portion of surface whose state is tobe studied, the principle of said method being such that the quotient ofthe indications provided by the two photoelectric cells ischaracteristic of a given state of surface and that the indicationprovided by the photoelectric cell corresponding to the beam which isdeflected by the cube provides the albedo of a given surface state andcolor.

A further object of the invention is to provide an apparatus forcarrying out said method, said apparatus being characterized in that itcomprises a stabilized stationary light source, a collimator fordelivering a beam of parallel rays from said source, a support fordisposing a substantially flat portion of surface at an oblique anglewith respect to said beam, a socalled object-grid which is parallel tothe lens of said collimator on the downstream side thereof and mountedacross said parallel beam, a centered optical system, a Lummer cubemounted at the downstream focal point or image focal point of saidcentered system, a so-called image-grid which is positionally adjustablein its plane, the two grids being located in the anti-principal planesof said centered optical system, two photoelectric cells so arranged asto receive respectively the direct beam and the deflected beam omittedby said Lummer cube and two variable diaphragms placed across saiddirect and deflected beams.

Further properties and advantages of the present invention will becomeapparent from the following description which is given with reference tothe single accompanying FIGURE and in which one embodiment of theapparatus according to the invention is given by way of explanation andnot in any limiting sense.

The accompanying figure is a diagram whose plane is definedby theprincipal axis of the beam of parallel rays emitted by the collimatorand by the principal axis of the beam of parallel reflected rays.

The apparatus in accordance with the invention as illustrated in thisfigure comprises a stationary stabilized light source 1, a collimator(lens 2 and variable slit 3), an objectgrid 4, a stationary support 5which is intended to receive a surface 6. In order to simplify theexplanation of the operation of the apparatus, it will be assumedhereinafter that said surface is flat (firstly a surface whichconstitutes approximately a perfect mirror and secondly a surface whosestate is to be determined), a centered optical system 7, a Lummerdividing cube 8, an image-grid 9 which is identical with the object-grid4, two photoelectric cells 10 and 11, two variable diaphragms l2 and 13which serve to balance said photoelectric cells and two convergentlenses l4 and 15 which serve to focus the light beams onto said twophotoelectric cells.

Each photoelectric cell 10 and I1 is connected to a galvanometer or to acomputer (not shown).

The grids 4 and 9 are disposed in the anti-principal planes of thecentered system 7, said planes being located by definition on each sideof said centered system at distances which are respectively equal totwice the object focal distance and to twice the image focal distance ofsaid centered system 7.

The Lummer cube 8 is placed at the image focal point of said centeredsystem.

By virtue of an arrangement of this type, the operation of the apparatusaccording to the invention is as follows First stage the surface 6 beinginitially a surface which constitutes approximately a perfect mirror,the stabilized light source 1 illuminates the slit 3 of the collimator;the emergent beam of parallel rays 16 passes through the object-grid 4.

The beam is reflected from the flat surface 6 in a bundle of parallelrays 17 and, after having passed through the centered optical system 7,produces a convergent beam 18 which is focused at F, namely the imagefocal point of the centered system 7 which produces an image of the grid4 on the other side of the point F.

By virtue of a conventional property of centered optical systems, theimage of an object 4 which is located in the antiprincipal object planeof the centered system 7 is formed in the other anti-principal plane ofsaid system and is equal to said object and inverted.

In the present case, the image of the grid 4 is consequently formed inthe plane of the grid 9.

Since the surface 6 is approximately a perfect mirror, the image appearsas the replica of the first grid.

Since the image-grid 9 is so adjusted that the gaps of said grid arelocated on the path of the different light beams which are transmittedto said grid 9 from the object-grid 4, the photoelectric cell 10receives the total quantity of light which has reached the grid 9.

One-half the light intensity of the beam 18 is deflected towards thecell 11 by the Lummer cube 8.

In order that the two photoelectric cells 10 and 11 should deliveredstrictly equal currents in respect of equal levels of illumination, saidcells are balanced by means of the diaphragms l2 and 13.

The image-grid 9 is then displaced in its plane so that the bars of saidgrid are located on the path of the light beams which fall on said grid.In consequence, no light falls on the photoelectric cell 10.

Second state the perfect mirror 6 is replaced by the surface to bestudied. By virtue of a diffusion phenomenon which arises from theroughness of said surface, a certain quantity of light then passesthrough the grid 9, this quantity being a function of the roughness, andthe photoelectric cell 10 is therefore excited. In actual fact, theintensity of the light which passes through the grid 9 is a function notonly of the roughness of the surface under study but also of its colorwhilst the intensity of the light which is deflected by the Lummer cube8 towards the photoelectric cell 11 depends only on the color of saidsurface,

Thus, if I designates the intensity of the light which is reflected fromthe surface 6, a designates a coefficient which is a function of thecolor of said surface and b designates a coefficient which is a functionof the roughness, it is apparent that the quantity of light which fallson the photoelectric cell 10 is 1/2 a b, while the quantity of lightwhich falls on the photoelectric cell 11 is 1/2 a. The quotient of saidintensities therefore has the value b and consequently depends only onthe roughness of the surface 6.

Since the electric current delivered by said photoelectric cells areproportional to the light intensities, it is apparent that the quotientof the indications supplied by said cells is a function only of theroughness of the surface 6 and is in no way dependent on its color.

So far as the photoelectric cell 11 alone is concerned, this celldelivers in respect of a surface 6 having a given color a current whichis proportional to I and therefore also proportional to l/l (I, beingthe intensity of light which impinges on the surface 6).

In other words, the photoelectric cell 1 1 serves to determine thealbedo of the surface 6 which has a given color.

In the above-described experiment, the study is carried out along apreferential axis by virtue of the fact that the object and the imageare provided by means of grids but it remains apparent that, dependingon the nature of the surface 6 under study, it would be possible toreplace the grids 4 and 9, for example, by square-mesh screens or bydevices having axes of symmetry of a higher order. Moreover, instead ofbeing flat, the surface 6 can be only substantially flat for example, itwould be possible to make use of a cylindrical surface having a longradius of curvature finally, instead of being stationary, the surface 6could be endowed with continuous motion.

It is readily apparent that this invention has been described in theforegoing solely by way of explanation without any limitation beingimplied and that any detail modifications could accordingly be madetherein without departing either from the scope or the spirit of theinvention.

We claim:

1. A nondestructive method for measuring the state of surfacesconsisting of the steps of projecting at an oblique angle onto asubstantially flat portion of surface constituting an approximatelyperfect mirror a beam of parallel rays of stabilized intensity, placingan object-grid at right angles to the axis of said beam, placing acentered optical system across the reflected beam of parallel rays andat right angles to the axis thereof, placing a Lummer dividing cube atthe downstream focal point or image focal point of said centered system,said Lummer cube emitting two beams having the same light intensity,directing one beam in the line of extension of the incident beam,deflecting the other beam through with respect to the first beam,placing across said direct beam and at right angles to the principalaxis thereof an image-grid identical with the object-grid and capable ofsmall displacements in its plane, locating two grids in theanti-principal planes of said centered optical system, said image-gridbeing locked in position so as to permit the light beams emitted by theobjectgrid to pass exactly through said image-grid, focusing said directbeam and said deflected beam each onto a photoelectric cell, adjustingsaid two photoelectric cells to supply equal currents under the actionof the light beam on the Lummer cube, displacing the image-grid in itsplane to stop all light beams emitted by the object-grid, and thenreplacing the portion of surface functioning as a perfect mirror by theportion of surface whose state is to be studied, the quotient of thecurrents from said two photoelectric cells being characteristic of agiven state of surface and the current from said photoelectric cellcorresponding to the beam which is deflected by said cube providing thealbedo of a given surface state and color.

2. An apparatus for measuring the state of surfaces comprising astabilized stationary light source, a collimator for delivering a beamof parallel rays from said source, a support for disposing asubstantially flat portion of surface at an oblique angle with respectto said beam, a so-called object-grid which is parallel to the lens ofsaid collimator on the downstream side thereof and mounted across saidparallel beam, a centered optical system, a Lummer cube mounted at thedownstream focal point or image focal point of said centered system, aso-called image-grid which is positionally adjustable in its plane, thetwo grids being located in the anti-principal planes of said centeredoptical system, two photoelectric cells so arranged as to receiverespectively the direct beam and the deflected beam emitted bysaidLummer cube and two variable diaphragms placed across said direct anddeflected beams.

3? UNTIED STATES PATENT OFFICE CERTIFICATE 0F CORRECTION Patent No. 3 I107 Dated y 6 1972 Inventor(5) Pierre M. Denis and Roger H. Guicherd Itis certified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

[73] Assignee: Societe Anonyme Heurtey 75 Paris 17 eme, France Signedand sealed this 10th day of October 1972.

(SEAL) Attest':

EDWARD M.F'LETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissionerof Patents

1. A nondeStructive method for measuring the state of surfacesconsisting of the steps of projecting at an oblique angle onto asubstantially flat portion of surface constituting an approximatelyperfect mirror a beam of parallel rays of stabilized intensity, placingan object-grid at right angles to the axis of said beam, placing acentered optical system across the reflected beam of parallel rays andat right angles to the axis thereof, placing a Lummer dividing cube atthe downstream focal point or image focal point of said centered system,said Lummer cube emitting two beams having the same light intensity,directing one beam in the line of extension of the incident beam,deflecting the other beam through 90* with respect to the first beam,placing across said direct beam and at right angles to the principalaxis thereof an image-grid identical with the objectgrid and capable ofsmall displacements in its plane, locating two grids in theanti-principal planes of said centered optical system, said image-gridbeing locked in position so as to permit the light beams emitted by theobject-grid to pass exactly through said image-grid, focusing saiddirect beam and said deflected beam each onto a photoelectric cell,adjusting said two photoelectric cells to supply equal currents underthe action of the light beam on the Lummer cube, displacing theimage-grid in its plane to stop all light beams emitted by theobject-grid, and then replacing the portion of surface functioning as aperfect mirror by the portion of surface whose state is to be studied,the quotient of the currents from said two photoelectric cells beingcharacteristic of a given state of surface and the current from saidphotoelectric cell corresponding to the beam which is deflected by saidcube providing the albedo of a given surface state and color.
 2. Anapparatus for measuring the state of surfaces comprising a stabilizedstationary light source, a collimator for delivering a beam of parallelrays from said source, a support for disposing a substantially flatportion of surface at an oblique angle with respect to said beam, aso-called object-grid which is parallel to the lens of said collimatoron the downstream side thereof and mounted across said parallel beam, acentered optical system, a Lummer cube mounted at the downstream focalpoint or image focal point of said centered system, a so-calledimage-grid which is positionally adjustable in its plane, the two gridsbeing located in the anti-principal planes of said centered opticalsystem, two photoelectric cells so arranged as to receive respectivelythe direct beam and the deflected beam emitted by said Lummer cube andtwo variable diaphragms placed across said direct and deflected beams.